Coupling device



Dec. 7, 1965 TETSUO YOSHIDA 3,222,621

COUPLING DEVICE Filed Jan. 8, 1962 4 Sheets-Sheet 2 I nvenlor Attorney Dec. 7, 1965 'TETSUO YOSHlDA COUPLING DEVICE 4 Sheets-Sheet 5 Filed Jan. 8, 1962 Inventor T. (Osman R Ho. -mq y m Yaw #1 Attorney Dec. 7, 1965 TETSUO YOSHIDA COUPLING DEVICE 4 Sheets-Sheet 4.

Filed Jan. 8, 1962 Attorney w an...

my q I i. Ho sN/ WE 1 United States Patent 3,222,621 COUPLING DEVICE Tetsuo Yoshida, Minato-ku, Tokyo, Japan, assignor to Nippon Electric Company, Limited, Tokyo, Japan, a corporation of Japan Filed Jan. 8, 1962, Ser. No. 164,749 Claims priority, application Japan, Jan. 28, 1961, 36/2,597 3 Claims. (Cl. 33326) This invention relates to coupling devices, and in parti'cular those commonly referred to as baluns, for feeding each of two common loads from two transmitters.

The split type balun shown in FIG. 1 has been conventionally used for the purpose of supplying common loads with two VHF transmitter outputs without mutual interference. In the standard application of this split type balun the first transmitter output, the second transmitter output, and the common loads are connected to a terminal 1, terminal 2, and terminals 3 and 4, respectively, with the result that the two transmitter outputs are split into two parts and supplied to the two loads. Since there is theoretically no coupling betwen terminal 1 and 2, if there is no reflection at the loads, the two transmitters do not mutually interfere. Due to the theory of reversibility, the power sources may also be connected to the terminals 3 and 4, and the loads to the terminals 1 and 2.

The balun of FIG. 1, however, has disadvantages as Will be seen. The frequency characteristics of the voltage standing wave ratios (VSWR) seen from the two input terminals are not alike; the one seen from the terminal 1 is better. Electric power supplied from terminal 1 propagates through the coaxial circuit consisting of the inner conductor 5 and the outer conductor 6 and passes through the 1/4 impedance transformer consisting of outer conductors 6 and inner conductor 7. Due to the nature of the transformer, the diameter of the inner conductor 7 is small, and heating is encountered during a large power transmission. Thereafter, the power passes through transformer 8 and generates voltage across both ends of slits 9 cut in the outer conductor of the transformer (see FIG. l(b)). Since these slits have the highest potential in the circuit the power transmission is limited by their breakdown voltage. On the other hand, when power is supplied from terminal 2, it passes through the 1/4 impedance transformer consisting of the inner conductor 6 and the outer conductor 10, and this construction is suitable for a large power transmission. However, due to two reasons, namely, that the impedance transformer is one stage, and that part 11 which forms a stub-circuit is inevitably inserted in parallel, it is difficult to make the frequency characteristics of the voltage standing wave ratio (VSWR) as seen from this input terminal broadband.

Hence it is an object of this invention to provide a coupling device which possesses an input terminal suitable for a large power transmission with a very wideband frequency characteristics of the VSWR, and an input terminal suitable for transmission of comparatively small power with comparatively narrow-band frequency characteristic of the VSWR.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, in which:

FIGS. 1(a) and 1(b) show longitudinal and cross sectional (along A-A) views, respectively, of a conventional split type balun.

FIGS. 2(a) and 2(1)) show longitudinal and cross sectional (along A-A') views, respectively, of a split type balun according to the invention;

3,222,621 Patented Dec. 7, 1965 "ice FIG. 2(0) is a transparent view of the device shown in FIGURES 2(a) and 2(b);

FIGS. 3(a) and 3(1)) show longitudinal and cross sectional (along A-A) views, respectively, of a modified embodiment using symmetry in the lower power input;

FIG. 3(a) is a transparent view of the device shown in FIGURES 3(a) and 3(b);

FIG. 4 shows still another modification of the invention depicted in FIGS. 2(a) and 2(b); and

FIGURE 4(1)) is a transparent view of the device sown in FIGURE 4.

Turning now to the invention, and in particular to FIGS. 2(a) and 2(1)), a large power source, a small power source and loads are connected to a terminal of lines 12, line 13, and lines 14 and 15, respectively. The power supplied from the terminal line 12 propagates through a coaxial circuit consisting of an outer conductor 16 and an inner conductor 17, the latter in turn being coupled at a point 18 in series with an open-end coaxial circuit, of approximately 1 /4 in length, consisting of the inner surface of the inner conductor 17 as an outer conductor and an inner conductor 19. Furthermore, the inner conductor 19 is connected at the point 18 to an impedance transformer, the inner conductor 20 of which is divided into two prongs, the prongs being connected to inner conductors 21 and 22 of the terminal line 14 and 15, respectively. The outer conductor 16 of the terminal line 12 is connected to outer conductors 23 and 24 of the terminal lines 14 and 15, respectively. On the other hand, an outer conductor 25 of the terminal line 13 which penetrates cover 26 is connected to the junction of one prong of 20 and 21 and the inner conductor 27 of the terminal line 13 is connected to the junction of the other prong of 20 and 22. If the load impedance connected to the terminal lines 14, 15 and the input impedance of the terminal line 12 are all 50 ohms and if the wavelength of the central frequency used is 1 then the required matching is obtained. The frequency characteristic is remarkably improved when the lengths of the circuits having 17 and 19, 16 and 20, and 16 and 25 as outer and inner conductors are all 7\ /4, and when the characterisic impedances of these circuits are approximately 14.6 ohms, 35.4 ohms, and 85.3 ohms, respectively.

The coupling device of the invention is suitable for large power transmission, because the large power transmitting portion is not an inner conductor of a double coaxial circuit as is the case in FIG. 1. Also, the breakdown voltage between 17 and 19 can be made low, since the input impedance at point 18 is remarkably low (0 ohm at center frequency and only of the order of two ohms in case of 10% deviation therefrom). The problem of temperature rise can also be easily solved, because the diameter of 19 is relatively large. Furthermore, no breakdown voltage problem between the slits is involved, since no potential difference is generated across the split conductors of 20. Since electric power from the terminal line 12 is divided into two at the end of 20, namely into 21 and 22, and supplied to the loads in phase, no voltage is generated across 25 and 27 and no coupling with the terminal 13 is formed. On the other hand, the electric power from the terminal 13 is divided into 21 and 22, which are connected to the outer conductor 25 land the inner conductor 27, respectively, as is obvious from the drawing. This makes the phases of the voltages across 21 and 22 antiphase and generates a standing wave only across the conductors divided into two of 20, with the result that the power from the terminal line 13 does not appear at the terminal line 12. The input impedance of 13 can be adjusted arbitrarily by providing an impedance transformer in the coaxial circuit of 25 and 27. Since the frequency characteristic is related to the input impedance of the pronged conductor, when the conductor 20 divided into two is considered as Lecher wires with their ends short-circuited, it can be improved by increasing the characteristic impedance of the pronged part and making its length equal to A1 of the operating Wavelength. The conductor 20 may consist of a cylinder with slits cut as shown in the drawing, or it may consist of a pair of metal plates, with proper cross-sections, arranged in parallel.

FIGS. 3(a) and (b) show an improvement in the symmetry of the circuit by installing another conductor 28 symmetrically to the outer conductor 25 of the terminal line 13. In this case, it is required that the sizes of and the spacing between 25 and 28 are such that the impedance of the circuit with 25 and 28 grouped as one and 16 as the outer conductor is most favorable. The favorable impedance is 853 ohms, for example, when the nominal impedance is 50 ohms.

FIG. 4 shows an embodiment which has a two-step M4 wave impedance transformer. In this case, the open and coaxial circuit formed by 17 and 19 of FIG. 2 is reversed into an inner conductor 29 of the second impedance transformer. It is possible to make this part a multistage impedance transformer of three or more stages.

By using a coupling device of this invention, it is possible to obtain a coupling device of a wide band and a large power comparatively simply. The coupling device of this invention will be more useful than the previously described conventional coupling device. In particular, this invention enables the coupling of wide-band high power with narrow'band low power. The need for this type coupling arises more frequently than the reverse coupling which was provided by the prior art devices.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that is description is made only by way of example and not as a limitation to the scope of my invention, as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1. A device for transferring power between first and second terminals and third and fourth terminals, connected respectively to a high power source, a low power source, and two loads comprising:

(a) first and second coaxial line terminals and third and fourth coaxial line terminals, the four lines being arranged in a cross with the third and fourth terminal lines constituting colinear members thereof;

(b) said first terminal line comprising an outer couductor and a central conductor having several sections in series including: a split conductor section, which together with the adjacent port-ion of said outer conductor serves as an impedance transformer, a hollow cylindrical section, an inner conductor section positioned coaxially within at least a portion of but spaced from said hollow cylindrical section with at least a portion of said inner conductor extending beyond at least one end of said hollow section, the gap between the central and outer conductor of said first terminal line being in communication with the space between said spaced apart hollow cylindrical section and inner conductor section, said inner conductor section forming together with said hollow section an open ended coaxial line with said gap serving as the open end of said coaxial line;

(c) the central conductor of the said third and fourth terminal lines being connected respectively to the two adjacent ends of said split conductor section;

(d) the outer conductor of said second terminal line penetrating an extended shorted portion of the outer conductor of said first terminal line;

(e) and the central and outer conductors of said second terminal line being connected respectively to the central conductors of said third and fourth terminal lines.

2. The device as claimed in claim 1 in which the inner conductor of said hollow cylindrical section is coextensive with the open end coaxial line for wavelength, and the length of the split conductor is 4 wavelength.

3. The device is claimed in claim 1 further comprising an additional conductor parallel with the outer conductor of the second terminal line, said additional conductor penetrating the extended shorted part of the outer conductor of said first terminal line symmetrically with respect to the position of said outer conductor of said second terminal line.

References Cited by the Examiner UNITED STATES PATENTS 2,724,806 11/1955 Tillotson 333-26 FOREIGN PATENTS 770,406 3/1957 Great Britain.

ELI LIEBERMAN, Primary Examiner.

HERMAN KARL SAALBACH, Examiner. 

1. A DEVICE FOR TRANSFERRING POWER BETWEEN FIRST AND SECOND TERMINALS AND THIRD AND FOURTH TERMINALS, CONNECTED RESPECTIVELY TO A HIGH POWER SOURCE, A LOWER POWER SOURCE, AND TWO LOADS COMPRISING: (A) FIRST AND SECOND COAXIAL LINE TERMINALS AND THIRD AND FOURTH COAXIAL LINE TERMINALS, THE FOUR LINES BEING ARRANGED IN A CROSS WITH THE THIRD AND FOURTH TERMINAL LINES CONSTITUTING COLINEAR MEMBERS THEREOF; (B) SAID FIRST TERMINAL LINE COMPRISING AN OUTER CONDUCTOR AND A CENTRAL CONDUCTOR HAVING SEVERAL SECTIONS IN SERIES INCLUDING: A SPLIT CONDUCTOR SECTION, WHICH TOGETHER WITH THE ADJACENT PORTION OF SAID OUTER CONDUCTOR SERVES AS AN IMPEDANCE TRANSFORMER, A HOLLOW CYLINDRICAL SECTION, AN INNER CONDUCTOR SECTION POSITIONED COAXIALLY WITHIN AT LEAST A PORTION OF BUT SPACED FROM SAID HOLLOW CYLINDRICAL SECTION WITH AT LEAST A PORTION OF SAID INNER CONDUCTOR EXTENDING BEYOND AT LEAST ONE END OF SAID HOLLOW SECTION, THE GAP BETWEEN THE CENTRAL AND OUTER CONDUCTOR OF SAID FIRST TERMINAL LINE BEING IN COMMUNICATION WITH THE SPACE BETWEEN SAID SPACED APART HOLLOW CYLINDRICAL SECTION AND INNER CONDUCTOR SECTION, SAID INNER CONDUCTOR SECTION FORMING TOGETHER WITH SAID HOLLOW SECTION AN OPEN ENDED COAXIAL LINE WITH SAID GAP SERVING AS THE OPEN END OF SAID COAXIAL LINE; (C) THE CENTRAL CONDUCTOR OF THE SAID THIRD AND FOURTH TERMINAL LINES BEING CONNECTED RESPECTIVELY TO THE TWO ADJACENT ENDS OF SAID SPLIT CONDUCTOR SECTION; (D) THE OUTER CONDUCTOR OF SAID SECOND TERMINAL LINE PENETRATING AN EXTENDED SHORTED PORTION OF THE OUTER CONDUCTOR OF SAID FIRST TERMINAL LINE; (E) AND THE CENTRAL AND OUTER CONDUCTORS OF SAID SECOND TERMINAL LINE BEING CONNECTED RESPECTIVELY TO THE CENTRAL CONDUCTORS OF SAID THIRD AND FOURTH TERMINAL LINES. 